The present invention pertains to apparatus and methods for generating a LOAD signal so that enhanced display modules can be used in a vending machine. In particular, the invention generates a LOAD signal from four available interface input signals for the enhanced display module.
Hundreds of thousands of vending machines exist in the field, and more are being manufactured each day. Most have four digit displays to inform customers of the value of the coinage inserted, and at least two manufacturers have standardized on a four wire interface that connects the vending machine controller (VMC) to the four digit display module. Each of the four digits consists of a seven segment display element, and the display module utilizes the following interface signals:
POWER (+5 Volts DC)
DATA (Serial data to the display)
CLOCK (Serial data shift clock)
GROUND (0 Volts)
The display capability of a vending machine can be expanded by replacing the seven-segment, four digit display module with an enhanced display module. The enhanced character display module, which typically comprises eight or more characters with a fourteen segment configuration of light emitting diodes (LED""s) or a dot matrix configuration, would provide the ability to display both numeric and text information.
Several suitable display modules are currently available, but require an additional interface signal, called a xe2x80x9cLOADxe2x80x9d signal, to differentiate between shifting the serial data into the module and loading it into the internal display memory. Thus, the LOAD signal must somehow be provided in order to retrofit such low cost enhanced display modules to existing vending machines, or to use them in the manufacture of new vending machines containing standard vending machine controllers (VMC""s). The vending machine control boards currently in use cannot generate such a LOAD signal, and thus a software solution for upgrading to enhanced character display modules does not exist.
The present invention pertains to low-cost apparatus and methods for generating a LOAD signal from the four available interface signals available from the VMC. Thus, a standard VMC providing four input signals can be utilized in conjunction with an enhanced character display module.
In one implementation according to the invention, the apparatus includes an enhanced display module requiring at least five input signals including POWER, CLOCK, DATA, GROUND and LOAD. An inverter is connected to the CLOCK signal, and a LOAD flip-flop is connected to the inverter and to the DATA signal line. The inverter and the LOAD flip-flop generate a LOAD signal for input to the enhanced display module.
In another implementation, a display module includes an enhanced display means and an interface circuit. The interface circuit generates a LOAD signal for input to the display means. The interface circuit may be a clock pulse counter circuit means for counting the eighth transition of a CLOCK input signal to generate the LOAD signal. Alternately, the clock pulse counter circuit may be a one-shot circuit that is triggered by the eighth transition of the CLOCK signal. Further, the interface circuit may be a missing clock detector circuit for sensing stoppage of a CLOCK signal and for generating the high state of the LOAD signal.
In yet another implementation, a display module for a vending machine includes an enhanced display means, a unidirectional component connected to a POWER input signal and a capacitor connected to the unidirectional component and to the display means. In this configuration, the VMC pulses the POWER signal momentarily so that the LOAD signal is generated by the capacitor for the display means.
A novel technique for generating a LOAD signal for an enhanced display module is also described, which uses at least one of four interface signals generated by a vending machine controller. The technique includes generating and validating a DATA signal, shifting bits of data for a display segment into the display element on the rising edge of the CLOCK signal if the DATA signal is valid, inverting the CLOCK signal and latching the DATA signal to generate a LOAD signal, and loading data for a segment into the display element memory.
Other apparatus and methods fall within the scope of the invention which apparent from the figures and the detailed description below.